The present invention relates to an incandescent lamp in which a transparent metal oxide film formed on the outer surface of a bulb has improved optical characteristics and does not separate from the bulb surface.
An incandescent lamp is known in which a transparent metal oxide film is formed on the outer surface of the bulb for bulb protection and infrared ray reflection. In consideration of uniformity of the film, productivity and cost of the lamps, such a metal oxide film is generally formed by a method in which an organic metal compound is applied on the outer surface of a bulb and is baked at a high temperature for decomposing the compound and converting the film into a thin metal oxide film.
When a lamp is turned on/off a number of times, separation of the metal oxide film tends to occur. Film separation is particularly notable in the case of a multilayered film such as an infrared ray reflection film.